As a related-art hemispherical resonator gyro, for example, there is known a vibratory rotation sensor disclosed in Patent Literature 1. A principal mechanical system configuration of this vibratory rotation sensor includes a hemispherical resonator, forcers, and pick-offs. The forcers are used to excite a first-order resonance mode on the hemispherical resonator, and the pick-offs are used to detect a phase change of the resonance mode, to thereby detect a rotational angle in a sensor measurement axis direction.
On the other hand, an electric system and a control system of this vibratory rotation sensor are constructed by four functions including (1) a reference phase generator, (2) first-order resonance amplitude control, (3) quadrature vibration control, and (4) phase angle detection of the first-order resonance mode. A description is now given of the functions (1) to (4).
First, through use of a phase locked loop (PLL) implemented in the reference phase generator, the first-order resonance frequency of the hemispherical resonator is locked based on detection signals output from the pick-offs, and further, various reference phase signals are generated. The detection signal output from the pick-off is demodulated based on the reference phase signal generated by the reference phase generator, and is translated to amplitude of the first-order resonance mode and a nodal quadrature vibration excited in the hemispherical resonator.
In the first-order resonance amplitude control, based on the reference phase signal generated by the reference phase generator, a square wave voltage applied to the forcer is controlled so that the amplitude of the first-order resonance mode excited in the hemispherical resonator is a constant value set in advance.
In the quadrature vibration control, through control of a DC voltage applied to the forcer so as to add a negative spring stiffness to an orthogonal axis displaced by 22.5 degrees with respect to a wave antinode phase angle of the first-order resonance mode, the amplitude of the nodal quadrature vibration is suppressed to zero so as to realize a state in which only the first-order resonance mode is excited in the hemispherical resonator.
Finally, in the phase angle detection of the first-order resonance mode, a wave antinode phase angle of the first-order resonance mode excited in the hemispherical resonator is calculated, and the rotational angle in the sensor measurement axis direction is detected by multiplying a change amount of the phase angle by a scale factor unique to the hemispherical resonator.
As another example of the related-art hemispherical resonator gyro, for example, there is known a control circuit for a vibratory gyroscope disclosed in Patent Literature 2.
In this control circuit for vibratory gyroscope, the first-order resonance mode excited in the resonator is considered as a composition of two traveling waves traveling clockwise and counterclockwise on the resonator in a circumferential direction thereof, and based on detection signals output from pick-offs, a reference phase signal is generated for each of the traveling waves by a phase locked loop (PLL).
Further, in order to correct a damping of a resonator vibration so as to maintain a vibration amplitude of each of the traveling waves to be a constant value set in advance, and to efficiently excite the first-order resonance mode on the resonator, based on the reference phase signal, a forcer application voltage is controlled under a state in which the phase is advanced by 90 degrees with respect to a radial displacement of each of the traveling waves.
Finally, from a phase difference of the reference phase signal relating to each of the traveling waves generated by the phase locked loop (PLL), the wave antinode phase angle of the first-order resonance mode excited in the resonator is calculated, and a change amount of the phase angle is multiplied by a scale factor unique to the resonator, to thereby detect the rotational angle in the sensor measurement axis direction.